linux-kernel - Re: [PATCH v2 0/7] Introduce bus firewall controller framework

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Message-ID: <7f54ec36-8022-a57a-c634-45257f4c6984@st.com>
Date:   Tue, 28 Jan 2020 16:46:41 +0000
From:   Benjamin GAIGNARD <benjamin.gaignard@...com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     "broonie@...nel.org" <broonie@...nel.org>,
        "robh@...nel.org" <robh@...nel.org>,
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        Loic PALLARDY <loic.pallardy@...com>,
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Subject: Re: [PATCH v2 0/7] Introduce bus firewall controller framework


On 1/28/20 5:36 PM, Sudeep Holla wrote:
> On Tue, Jan 28, 2020 at 04:37:59PM +0100, Benjamin Gaignard wrote:
>> Bus firewall framework aims to provide a kernel API to set the configuration
>> of the harware blocks in charge of busses access control.
>>
>> Framework architecture is inspirated by pinctrl framework:
>> - a default configuration could be applied before bind the driver.
>>    If a configuration could not be applied the driver is not bind
>>    to avoid doing accesses on prohibited regions.
>> - configurations could be apllied dynamically by drivers.
>> - device node provides the bus firewall configurations.
>>
>> An example of bus firewall controller is STM32 ETZPC hardware block
>> which got 3 possible configurations:
>> - trust: hardware blocks are only accessible by software running on trust
>>    zone (i.e op-tee firmware).
>> - non-secure: hardware blocks are accessible by non-secure software (i.e.
>>    linux kernel).
>> - coprocessor: hardware blocks are only accessible by the coprocessor.
>> Up to 94 hardware blocks of the soc could be managed by ETZPC.
>>
> /me confused. Is ETZPC accessible from the non-secure kernel space to
> begin with ? If so, is it allowed to configure hardware blocks as secure
> or trusted ? I am failing to understand the overall design of a system
> with ETZPC controller.

Non-secure kernel could read the values set in ETZPC, if it doesn't match

with what is required by the device node the driver won't be probed.

Benjamin

>
>> At least two other hardware blocks can take benefits of this:
>> - ARM TZC-400: http://infocenter.arm.com/help/topic/com.arm.doc.100325_0001_02_en/arm_corelink_tzc400_trustzone_address_space_controller_trm_100325_0001_02_en.pdf
>>    which is able to manage up to 8 regions in address space.
> I strongly have to disagree with the above and NACK any patch trying
> to do so. AFAIK, no system designed has TZC with non-secure access.
> So we simply can't access this in the kernel and hence need no driver
> for the same. Please avoid adding above misleading information in future.
>
> --
> Regards,
> Sudeep
>